This discussion presents information from an article I published in the Fall 1988 issue of American Angler and Fly Tyer. The information is never obsolete as long as we use toxic solvents in the art of dressing flies. Liquid organic solvents (let's assign the acronym LOS to save space) that we use in dispersing agents, adhesives, cements, lacquers, and paints are in focus here. It is appropriate to be aware of the properties, effects, and give tips for safe storage and use of these hazardous materials.

A solvent dissolves or disperses other substances. It therefore is the major compound in any solution. This is the case with that bottle of "liquid fly tier" on your bench, whether it contains something dissolved in a LOS or water. A good example is "Flexament." It's made from Shoe Goop which contains enough solvent to give it the consistency of a (yuck!) booger. A booger's solvent is water, Shoe Goop's is tetrachloroethylene. I won't mention the former again. We add even more solvent to thin Shoe Goop for "judicious use" (Thanks for the term, Marvin!) in setting "recalcitrant materials" (Again, thanks, Marvin!) to gain beauty and symmetry in our dressed products.

Let's now turn to the physical and detrimental properties of LOS. The LOSs are hydrocarbons, some of which are halogenated (bromated, chlorinated or fluorinated). Others can be sulfated, nitrated or bonded with other elements or __compounds. They all are nasty if ingested. All LOS obey physical laws, which when understood provide ways to minimize detrimental effects of their vapors. Evaporating solvents exert a vapor pressure on their surroundings. That is why you can smell them. They will continue to evaporate until the atmosphere above them is saturated and exerts an equivalent partial pressure. That is why you cap their containers. The concentration of LOS at saturation depends on temperature and pressure. The vapor pressure of all LOS increase about 3%for each rise in temperature per degree Fahrenheit. The solvent vapor state is central to this discussion because respiration of their vapors is the primary mechanism for exposure.

Now let's look at the surprising amount of vapor that can be produced by a small amount of LOS. Let's say your bottle of "liquid fly tier" contains 40 grams of contents. Of this, 75%, or 30 grams is a LOS. Avogadro's law of molar volumes states that a gram molecular volume of gas will occupy 22.4 cubic liters. If the LOS is toluene and it all evaporates, its vapors will occupy around a cubic foot. Disperse this amount in the atmosphere around your tying bench repeatedly and you are heading for problems. No, the problems are not related to the expense of replacing the "liquid fly tier." They are the cumulative effects of ingesting LOS vapors, also called chronic effects. These effects impact the respiratory system if the vapors accumulate in the lungs to act as asphyxiants. If they pass from the lungs to the central nervous system, they can have narcotic or anesthetic effects. If they pass to organs they can also have detrimental effects. Organs that process wastes, the kidneys and the liver are in particular peril here. These are the overwhelming reasons why not to allow repeated exposure to evaporated LOS around your tying bench.

Now, given that many solvents will disperse cement, lacquer or pigment, how does one select the safest? The best information is obtained by consulting a toxicologist in your state department of health office. Toxicologists define the term threshold limit value (TLV), the mean vapor concentration in parts per million (ppm) a person can be exposed to without ill effects over a forty hour week. Toxicologists recommend that only solvents with TLVs above 500 ppm can be used safely in a well ventilated area. But vapor pressure comes into consideration, because it is the main mechanism by which vapors are ingested. Using TLVs and characteristic vapor pressures of each solvent, toxicologists calculate (I won't bore you with that calculation) vapor hazard ratios (VHRs) which take into account volatility as well as toxicity. The VHRs combined with TLVs give the most useful information for selecting the safest solvent for a particular task. To illustrate, here's a short table.

· Choose the least hazardous solvent to do the job
· Avoid breathing solvent vapors
· Avoid skin contact

Let's hold here to say that LOSs also adsorb through the skin. Wear rubber gloves when you handle them in large quantities. Another important point is that LOS transpire through such as polyethylene and polypropylene. The mechanism is similar to skin adsorption. That means storage in glass bottles in best for liquids containing LOS. Afraid the glass will break when dropped? Wrap the bottle exterior with masking tape.

· Use LOS only in ventilated areas
· Store LOS in as low as temperature surroundings as possible
· Clean up spills immediately

Let's hold again! Spills increase the surface area of LOSs. That makes for two dangerous consequences: increased evaporation and flammability because of the bigger surface area of a spill. Don't mess with Ma Nature. Stop operations and clean it up!

· Practice good hygiene habits at your work bench (No nose pickin' or finger lickin')
· Consult a toxicologist before acquiring a material with an unfamiliar LOS

Happy and hazard-minimized fly dressing to you!